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Batwings on a mill


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Keepers thread on cutting thickmetal got me thinking whether or not I could cut something like a batwing on my mill. It occured to me that I could cut the radiuses with a rotary table, and connect the circles with straight lines. I thought I'd try it on a piece of wood just to go through the motions once. It turned out to be even easier than I thought it would be, and I cant see why it wouldnt work on a piece of plate steel. When I get a little more free time I'm going to try it.

I got the picture from a Total Performance plan, and started by drilling the holes.

I bolted the piece through the center of the rotary table, lined the cutter up and spun it around.


Next I spun the rotary table untill the straight lines lined up with either the X ro Y axis, and cut them.


Everything is cut except the axle hole, if I were doing this for real I would be making a pair and would bolt both pieces down back to back and cut both at one time.

If the piece were rough cut first the actual milling on one of these could be done in less than half an hour. If all the rotary table settings were recorded it would be even faster.
The only thing I am unsure of is how stable my little rotary table will be cutting steel, that could slow things down some, but I still think it will work. A bigger rotary table and a metal band saw are still on my christmas list, I have been watching Craigs list and have seen a couple nice older USA made band saws in the $100 range, just a little farther than I want to drive. Sooner or later something will come up.
Very nice. Is that the nice big machine you just picked up?

After all was said and done I ended up using the diegrinder and a zip disc. A lot of cleanup work but so far so good. Should have some finished pieces this week as I am off until the 29th :welcome:
Looks good to me. If you do it this way, use a roughing mill cutter instead of the one shown in the thread. The finish isn't as smooth, but it's easy to clean it up after you're done. The roughing cutter will look something like this:

The cutting geometry is such you'll be able to cut faster with less effort. Make sure to use lots of oil and keep the spindle speed slow.

The forces involved here are very high when you stack these two parts for machining. So you might find a couple of spots opposite of each other on the edges to tack weld the two parts together. This will help keep them together until you're done. Then grind off the tack welds to separate them for final finishing.

Just my two pennies.

very nice martin. i would expect nothing less from a bout craftsman. giv e some thought to making the tow wings as one piece and cutting them in half when you are done with the profiles.

now for those of use without one of those wonderful metal giants, when i cut pieces out on the band saw, i drill 1/2 or 5/8 holes in the inside radius' first. this cuts down on the finish work and also allows you to turn the piece when the blade is in the hole to continue cutting. also laying the part out on both sides allows you to turn the piece over if need be.

another tip is to make your patterns on posted paper and hold them in place with magnets when tracing. it's nice to have several colors of sharpies for this.

I have done similar projects on small tables. I would recommend that you take your time, know that climb milling will make cutting more unpredictable, and run with the locks on the rotary table set snug to "very firm".
With a little practice you can turn out decent parts, just don't expect to make a living with it. Good Luck.

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